In the approximately 2.5 million American men diagnosed, the experience of prostate cancer can exact a psychological and physical toll. The period following radical prostatectomy or radiation therapy for localized prostate cancer is marked by relatively rapid changes physical functioning and can be a critical period marked by increased depression and poor psychological adjustment for men. In the context of cancer, depression can compromise important health outcomes. However, little research has sought to examine the unfolding risk and occurrence of depression following prostate cancer treatment. A primary goal of this research is to specify and test a theoretically-driven model of how psychological and contextual vulnerabilities shape trajectories of depression in the year following prostate cancer treatment. This project calls upon stress and coping, psychoneuroimmunology, and emotion regulation theories and research to investigate the causes and mechanisms of depression among prostate cancer patients. This research seeks to accomplish three specific aims. Aim 1 is to investigate how psychological and contextual vulnerabilities (including cancer-related and general stressors), emotion-regulating processes, and proinflammatory cytokines shape trajectories of depression in men with prostate cancer in the year following treatment. Aims 2 and 3 will examine emotion regulating processes and proinflammatory markers as proximal mediators of psychological and contextual vulnerabilities' effects on depression, respectively. We will accomplish these aims using a longitudinal research design set to begin prior to initiation of cancer treatment in 150 ethnically-diverse men, with subsequent assessments at 1 and 2 months post-treatment, and every 2 subsequent months through month 12. Blood sample collection, validated questionnaires and interviews, and evaluations of emotionally-expressive behaviors will be administered. This approach will allow for identification of which features characterize patients in whom depression is persistent and to whom to target intervention. Understanding the patterns and etiologic processes of depression as it is experienced by prostate cancer patients will have implications for the assessment and treatment of depression and the development of efficacious interventions